Nonsetting ammonium nitrate explosive composition and process



Patented Nov. 19, 1940 UNITED STATES PATENT OFFICE Nonsarrmo nMMoNrUM NITRATE 'Ex- ..PLOSIVE COMPOSITION AND raocnss Tho rvald w. Haul! and Harrison 11. Holmes, 'Woodbury, N. J., assignors to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware .No Drawing. Application March 4, 1939, Serial No. 259,798

9 Claims.

This action may cause serious trouble because the presence of 'moisture not only tends to make the explosive composition insensitive, but also induces setting.

ticable.

Those engaged in the art have made comprehensive experiments in an effort to overcome the setting of explosive ingredients but have not heretofore been entirely successful with compositions containing significant quantities of ammonium nitrate. i

The object of the present invention is an ainmonium nitrate explosive which does not set or harden' during continuous storage. A further object is a nonsetting ammonium nitrate especially adapted to explosive compositions and others wherein; setting is a (disadvantage. An additional object is 'a'novel and improved 'anti- 8 setting agent. A still further object is a method for preparing said nonsetting agent and/or a method for applying the same to the ammonium nitrate to impart anti-setting properties thereto. The foregoing objects are accomplished by uti- 85 lizing as the anti-setting agent in ammonium nitrate explosives and other ammo um nitrate compositions, the product which results when ammonium nitrate is reacted with zinc oxide, preferably with the removal of water. ,So far as 40 is'now known this product is believed to be zinc tetraminoenitrate, apparently having the iormula Zn(NI-I3)4(N0a)z. However, we do not intend to be bound 5 lely by this theoretical explanation of the nature of the product.

This reaction product is preferably employed as a coating on the ammonium nitrate particles and maybe applied to ammonium nitrate for explosive and other compositions by means of the process described in the following examples, which of course are not intended to limit the invention, but rather are cited as specifice embodiments thegeof.

Example I A solution was prepared which was saturated with both m nitrate and zinc oxide.

This "latter, if r sufllciently 16 marked, renders the use 9f the explosive imprac- The solution was prepared at 80 C. and maintained at this temperature for 4 hours, and then cooled to room temperature, whereby precipitation of a quantity of solid was efiected. This precipitate was separated and heated at 5 C. until dry, after which 1% of it by weight was added to hot, dry granular.'ammonium nitrate, the mixture being thoroughly agitated during the subsequent cooling procedure. Small scale tests showed that the finished product possessed un- 10 usually good non-caking properties.

Example I! A saturated-solution of ammonium nitrate at C. was prepared, and an amount 01 zinc'oxide 1 corresponding to 2% of the weight of the am-' moniur'n nitrate present in the solution was added slowly. The zinc oxide dissolved in the solution, which was maintained at 75 C. for an additional 4 hours. Following this, it was cooled to room 20 temperature, during which treatment white crystals were precipitated. These were separated and v heated at 70 C. until dry. 7% of this material was added to hot,.dry ammonium nitrate and the mixture thoroughly agitated during the subse- 25 quent cooling procedure. The final product not only exhibited excellent non-caking properties, but in addition compared favorably with untreated ammonium nitrate with respect to hygroscopiclty.. a

It will be understood that the method of uti-- lizing this anti-setting or non-caking material is not restricted to the addition of the dry reaction product to finished dry ammonium nitrate. Instead the reaction product at the time of addition may contain moisture, which is eliminated by drying. The reaction product likewise may be formed in situ, that is to say by adding the requisite amount of zinc oxide to granular ammonium nitrate and heating the mixture, thereby causing 40 the reaction product to form while simultaneously eliminating the water resulting from the reaction. Such procedure is illustrated in the following example.

Example III 45 showed the moisture content of the treated ammonium nitrate to be within the desired range. Moreover, subsequent storage tests failed to show any increase in moisture content which could be ascribed as due to the water formed in the reaction of zinc oxide with ammonium nitrate, therefore indicating that said reaction had been completed. This material exhibited excellent antisetting properties.

Likewise, the reaction product may be employed advantageously in those cases where a melt of ammonium nitrate is granulated by means of a graining kettle, the zinc oxide or reaction product being added to the hot granular ammonium nitrate. Substantially uniform distribution of the reaction product over the ammonium nitrate may be efl'ected by agitation of the mixture while in the graining kettle. It will be clear that the reaction product need not be dry, but instead may contain water at the time of its addition to the ammonium nitrate,'it being essential only that the treated ammonium nitrate mixture be dried before use.

Ammonium nitrate thus treated is quite desirable for explosive compositions because it permits formulations very high in ammonium nitrate content without danger that such compositions will become insensitive during storage, due to caking or setting of the material. Moreover, the reaction product of zinc oxide and ammonium nitrate is stable with respect to ammonium nitrate, hence does not react to yield undesirable products. In addition, ammonium nitrate-reaction product mixtures, when subjected to atmospheres of high humidity, with the attendant absorption of moisture, do not appear wet but instead maintain a perfectly dry appearance. This latter property is important because it decreases the tendency of the materials to separate, hence is favorable with regard to maintaining the homogeneity of the mixture.

The fact that this reaction product possesses such properties is quite unexpected, since it possesses a physical structure quite diflerent from those of recognized anti-setting agents, lcieselguhr, for example. Since the new antisetting agent is the reaction product of zinc oxide with ammonium nitrate, its subsequent addition to ammonium nitrate in effect represents the intimate contact of two materials inactive with respect to one another.

Although the invention is especially advantageous for producing nonsetting explosive compositions in particular, it should be understood that the invention includes within its scope the use of the ammonium nitrate for any purpose.

It will be apparent to those skilled in the art that many variations in our invention may be made without departing from the spirit or scope thereof. We intend, therefore, to be limited only in accordance with the following claims.

We claim:

1. An explosive composition of improved nonsetting properties comprising ammonium nitrate coated with zinc tetramino-nitrate.

2. An explosive composition of improved nonsetting properties comprising ammonium nitrate and the reaction product of zinc oxide with ammonium nitrate, in contact suiiiciently intimate to reduce the caking of said explosive composition.

3. An explosive composition of improved nonsetting properties comprising ammonium nitrate in intimate contact with the product resulting from the reaction of zinc oxide with ammonium nitrate. V

4. The explosive composition of claim 3, wherein the reaction product content is between 0.25 and 5.0% by weight of the ammonium nitrate content.

5. A method of preventing the caking of explosive compositions high in ammonium nitrate content, which method comprises reacting zinc oxide with ammonium nitrate, removing substantially all the water content from the product and adding-said product to the ammonium nitrate to be employed.

6. A composition comprising ammonium nitrate coated with the reaction product of zinc oxide with ammonium nitrate.

'7. A method of preventing the caking of ammonium nitrate, which comprises coating 'granular ammonium nitrate with the product resulting from the reaction between zinc oxide and ammonium nitrate.

8. A method of preventing the setting of ammonium nitrate, which comprises adding the reaction product of zinc oxide and ammonium nitrate to a melt of the ammonium nitrate, and

THORVALD W. HAUFF'. HARRISON H. HOLMES. 

